Printed circuit boards (PCBs) are the means of choice to interconnect a wide variety of electronic circuits and associated components into electronic or electro-mechanical assemblies capable of performing a nearly unlimited number of tasks ranging from ultra miniature surveillance devices to mainframe supercomputers. The PCB assemblies can range in size from several square millimeters to a square meter and beyond. An art form in PCB manufacturing is to reliably produce fine-pitched circuits of conductor material (typically copper; Cu) on physically large circuit boards such as 0.5 mm component pad spacing on a 32-layer 18″×24″ PCB; a feat presently attainable by only a select few PCB fabricators worldwide. This feat becomes nearly unattainable at a component pad spacing of 0.4 mm and smaller. Greatly facilitating sub 0.5 mm circuit geometries (e.g., device-under-test (DUT) pin-to-pin pitch) is the allowance of smaller/thinner PCBs.
Unfortunately, a small circuit board will rarely hold a large amount of circuitry. Further, the physically large circuit boards (e.g., load boards), which can hold a large amounts of circuitry and interfaces are expensive and may be an interface to complex equipment. In particular, in a test environment load boards may be used to interface to complex digital and analog signal analysis and test equipment.
For example, referring to FIG. 1, using the current technology as discussed above, in that a load board (or mother board) 100 has a socket 110 that mounts directly to mother board 100 using fasteners 112. A device under test (DUT) 115 having a certain ball grid array (BGA) spacing (e.g., 0.5 mm BGA) is mounted in the socket 110. Load board DUT and support electronics signals may be conveyed to off-board host instrumentation through various connector means 118 including spring loaded bed-of-nails pin arrays. The mother board may be substantially larger than the socket 110/DUT 115 (e.g., a 32-layer 18″×24″ PCB, as noted above). Although the mother board 100 can be physically large, the trace widths have to scale to match the spacing of the DUT 115 (e.g., 0.5 mm), at least in the mounting area of the DUT 115. However, as the BGA spacing gets smaller in newer components, the large mother boards 100 cannot scale to these smaller spacing requirements.
Additionally, the configuration of FIG. 1 has limited space for tuning components that are used for high frequency (e.g., RF) connections or other components requiring close DUT proximity. Accordingly, conventional direct mounted DUT/mother board configurations would also require complex and numerous board mounted connectors to obtain the RF signals off the DUT.